I think that's why I don't want to go back to my 20s again. I might have been a pert-breasted 21-year-old, presenting Fair Go, utterly certain the world was out there for me on a platter. But life is give and take.
All very well and good for me to devour experiences and opportunities. I had to learn to give back to keep the equilibrium. I hadn't yet learned that to enjoy the ups, you must know the pain of downs.
To be honest, there were very few downs. I lost my dad far too young. A couple of men didn't bend to my will, but that was hardly heartache, more wounded pride. And although my daughter and I did it tough financially for a while, it was entirely my own fault.
Really, when I look back, it has been a life full of fun and opportunity. I'm only looking back briefly.
It's like when I'm running a marathon or when I climbed Kilimanjaro. You look back only so you know how far you've come and that gives you the desire and the energy to keep going.
When I was 13, at Sacred Heart Girls' College, I had a teacher whose triceps were so flabby they would wipe the chalk off the blackboard.
We judgmental teenagers would watch the letters disappearing, appalled, and later, over marmite and cheese sandwiches at lunch, would agree that we'd all rather be dead than have arms like that.
But as everyone who reaches a half century knows, actually, we'd rather be alive with flabby bits than dead with firm skin.
Of course it's extraordinary watching yourself in physical decline: the hair or the lack of it; the skin tone; the fact you're seen as a safe person to be around rather than a dangerous rake on the make.
But that's okay. Because if you value your family, your friends and your health, your physical appearance is the least of your worries.
My 50th birthday on this planet started with the delivery of 50 balloons. They were from two very dear friends, both older than me.
They recently married after many years together and it was one of the most joyful, optimistic, loving weddings I have been fortunate enough to attend.
They encourage me to believe in new beginnings, no matter what your age.
My birthday lunch was at Soul in the Viaduct and to have my daughter home from England with her husband and my mum alongside me was the best present a woman can have.
To have your family a) alive and b) choose to be with you is an incredible gift.
Given that my birthday falls two days after Christmas, I seldom have a party because everyone is away.
But this year I had two close girlfriends in town. One is an old friend from 25 years ago. The other is a new friend. I didn't think I had the capacity to take in another friend but when people are right for you, you can always accommodate them.
The sun shone, the Viaduct looked a picture and Champagne flowed. And then, because I had taken one of the balloons with me to lunch, one that sang Happy Birthday in a particularly jaunty tone, one of the other patrons struck up conversation with our table.
He was a visiting Aussie, a former rugby international, and he was meeting Kiwi friends and business colleagues.
He encouraged them to sing Happy Birthday to me (which they did, in Maori, far more tunefully than my battery-operated balloon) then encouraged the restaurant to sing Happy Birthday (which they did, in English) and then sent a bottle of Champagne to the table.
By this time, I was dangerously close to being in a state that Pope Francis abhors in his Vatican bureaucrats.
Surely, though, you can have a papal dispensation for being bloated by your own magnificence on your birthday - and such a big birthday, too.
If this birthday was an indication of the fun and fabulousness you can have in your 50s, bring on the next 50 years.
• Kerre McIvor is on Newstalk ZB, Monday to Thursday, 8pm to midnight.
